In the air duct sector, and in particular in respect of their use in the automotive industry, the parts used for channelling air are known, said parts being formed by a hollow main body which has one or several coupler nozzles between its two ends, also called nipples, in order to branch the main duct for connection to other devices or pipes, said nipples being joined and connected to the main body.
The manufacture of parts from plastic material consisting of an internally hollow body and additional peripheral parts attached thereto is well known, such as for example, piping tubes, tanks or other enclosed hollow element that usually forms part of a motor vehicle. These types of connectors or nipples are often characterised by being precise shapes, thin thicknesses (even less than 2 mm) and with a very exacting precision and/or clearance in the joining area with the main body.
To obtain a hollow main body, a conventional extrusion/blow-moulding process is typically used while obtaining the other connectors attached to the main body, such as nipples, lugs, pipettes, including sensors, is performed in further steps by means of injection moulding, cutting processes etc.
In order to get the end product, a physical connection between the main body and the different connectors is required. This connection is made subsequently to the single part manufacturing process and by using supplementary processes, such as welding, manual clipping, etc.
In general, the type of aforementioned parts, obtained at various stages of the manufacturing process, have a substantial uncertainty in relation to the quality of the finished product, leading to an undesirably high number of rejects of the product due to the poor robustness of the process, which is linked to manual tasks and imperfect processes (welding and bonding), a fact that is particularly accentuated when the type of plastic to be used is of the soft type with a hardness of between Shore 5 and Shore 65.
Such flaws in the end product are often associated with defects at the joining of the nipples associated with the main duct.
In addition, another equally important drawback is the fact that the current manufacturing method involves a high cost arising, on the one hand, from the need for tools to perform the three processing processes (extrusion blow-moulding, mould injection and tooling intended for the joining of the multiple parts) and, on the other hand, the high cycle times due to each of the three manufacturing processes being completely independent from each other.
Several techniques aimed at resolving the aforementioned problems in the state of the art are known to the applicant. Such techniques can be essentially summarised using three methods:                1) Traditional method: This involves obtaining the main body of the duct by extrusion blow-moulding and the nipples by injection, in tooling and completely independent processes. In this way, once the two geometries have been obtained, they are joined by means of a welding process (hot plate, ultrasounds, etc.) which requires a machine and a specific tool for this part of the process. The main problem with this method is the increased cost resulting from the individual costs of the manufacturing subprocesses, quality control of the subprocesses, logistics of the actual process, greater need for floor space, cost of poor quality, etc., in addition to the problems arising from the parts not adequately supporting the service life for which they have been designed, especially when the plastic used has a hardness of between Shore 5 and Shore 65.        2) Integrated method: It is a variant of the above method, consisting of first manufacturing the nipple by injection and arranging it inside the mould of the extrusion blow-moulding process like an insert, such that the polymer would brace the part or insert during blowing such that the nipple remains fixed to the hollow main body obtained in the second process. The problem with this method is that a third external process is required, which internally communicates the nipple and the hollow main body. In addition, as the joining between the two geometries is done physically or by mechanical interference and not when hot (as the nipple has been produced in a separate previous step), the mechanical performance of said joining and flexibility in respect of the design are dramatically reduced, a fact which is greatly exacerbated when the material used has a hardness of between Shore 5 and Shore 65.        3) Method of extrusion blow-moulding and integrated injection: This relates to the technique of extrusion blow-moulding and injection in the same tool, but sequentially. This method is not applicable when the material used has a hardness of between Shore 5 and Shore 65 as the over pressure from the injection process on the geometry obtained by blowing deforms it making it invalid for final use.        
In this regard, the U.S. Pat. No. 5,198,174 describes obtaining additional radial supports for a tube from the application of an overmoulding process which consists of a first phase of production of the hollow tube by blow-moulding. Subsequently, the mould is modified to a second arrangement, and material is supplied thereto. Finally, the mould insert is modified to a third position which causes the material to be pressurised and form the embedded radial portion in the first previously blown portion.
Spanish patent no. ES 2104846 which discloses an integrated manufacturing process for the same type of components is also known. This process involves a first blow-moulding step in order to obtain the hollow body, the modification of the mould and the subsequent step of injecting a number of tabs affixed to the first body.
On the other hand, U.S. Pat. No. 6,793,870 and U.S. Pat. No. 5,266,262 refer to both processes of joining two components made from plastic material such that the hollow component was obtained in a first process. Subsequently, this formed part is inserted into a second mould where the process for obtaining the second component takes place, such that during the second process, a joining between both components is created.
Nonetheless, in spite of the advantages that the aforementioned processes may have in respect of the conventional manufacturing process, these also present a number of drawbacks:                They are not suitable for producing tubes less than 2 mm thick as the pressure in the second overmoulding process deforms the hollow main body.        They can be used in very technical materials (PA, PA6, PA66, PPS, PET, PBT, PEEK, etc.) usually reinforced, therefore not being suitable for processing other materials, such as soft thermoplastic elastomers, PP, PE or EPDM with a hardness of between Shore 5 and Shore 65.        The cycle time is high (about 30% higher than in traditional processes), due to it being the only way to minimise deformation during the process of filling during the over moulding phase, but which, on the other hand, affects the internal compacting of the manufactured part which makes it impossible to get a proper polymer structure. In particular, this aspect affects the final quality of the part as the overmoulded part is always aligned to the radial and/or axial axis of the hollow body.        The methods described above are not suitable for obtaining completely hollow parts and components, main body and protuberances, in one single manufacturing stage. They must always have an external mechanism that links the two cavities, whereas the system and method proposed here, the component or part obtained, is obtained completely unified in and during the same manufacturing process.        